Passive safety of vehicles refers to the performance of protection for occupants in case of accidents. In terms of automobiles, safety belts and air bags are fittings that are of great concern to the public for passive safety. However, the safety protection effect of air bags will be severely compromised and the occupant may even be injured when the air bags are released, if the seat belt is not fastened up correctly.
Seat belts used in automobiles are usually a sort of seat belts that will be locked up in case of emergencies. Before use, the seat belt can be pulled out easily. In the normally driving process, the seat belt retractor in the automobile exerts weak spring retraction force to hold the seat belt in position, and doesn't cause a sense of excessive pressure on the occupant. However, in the event of any crash and severe sway, the locking device will seize and lock up the seat belt immediately, to prevent the seat belt from pulled out further.
Nowadays, a sort of pre-tensioner restraining seat belts have been developed, which can tension up the seat belt further so as to effectively restrain the body of the occupant in the event of crash.
At present, many pre-tensioner seat belts employ a pyrotechnic principle, i.e., the so called “pyrotechnic seat belts”. The retractor of a pyrotechnic seat belt has a set of pyrotechnic means, which, when initiated, drives the retractor to rotate with blasting energy, and thereby attains a tensioning effect. Such a seat belt is usually used in combination with air bags. Usually, such a pre-tensioner seat belt has two functioning principles: it has the same function as conventional seat belts during light collision or hard braking. That is to say, when the seat belt is pulled quickly by force, the retractor will lock up, but will not initiate the pyrotechnic means. In that sense, the pyrotechnic means will function only when the collision reaches to a certain degree of severity. Moreover, the pyrotechnic means is of one-off type, which means it has to be replaced in a repair shop after it is initiated.
In a pyrotechnic seat belt apparatus, a gas generator is essential. In addition, the use of high pressure gas implicates that appropriate material and structure have to be used to ensure enough strength and leak-tightness during use. Moreover, a pre-tensioner seat belt will generate pretension force in the event of a crash, which is preset in the manufacturing process, and can't be adjusted to adapt to the body type of a specific occupant. Therefore, the safety protection performance of such a pre-tensioner seat belt apparatus is not satisfactory enough. In addition, such an apparatus must be integrated into the retractor, so as to apply the kinetic energy directly on the roller shaft for the seat belt. Hence, such an apparatus has drawbacks such as large size, complex design, high cost, and adjusting inconvenience, etc.
Some vehicles are fitted with a pre-crash safety system, which has a pre-tensioning function provided by an electro-dynamic mechanism. Thus, in such a pre-crash safety system, the seat belt can be reused. Of course, the number of reuse cycles is limited. If the limit is exceeded, the entire pre-crash safety system, including the pre-tensioner seat belt, has to be replaced. Though such a pre-crash safety system is reusable, it is difficult to replace. Moreover, since the system has to be controlled electronically, it also has drawbacks such as complex structure, inconvenience in replacement, high cost, low reliability, and poor applicability, etc.
In Patent Document No. GB2294866, a pre-tensioning apparatus that utilizes inertia for mechanical control is disclosed. The working principle of that apparatus is as follows: as shown in FIG. 17, in the normally driving state, an actuating rod 16 is not engaged with a mass block 17 firmly, but is engaged with a seat belt supporting member 47 instead; the seat belt supporting member 47 is wedged to a belt buckle 53 of the strap S of the seat belt, as shown in FIG. 17. In case the deceleration exceeds a preset safety limit, the mass block 17 will move forwards under inertial effect, and consequently the actuating rod 16 engages the mass block 17 in a concave-convex engaging manner and disengages from the seat belt supporting member 47, so that the seat belt supporting member 47 drives the strap S to move downwards and backwards in direction F, and thereby tensions up and restrains the seat belt at a restrained position.
The tensioning force provided by such a mechanical pre-tensioning apparatus depends on the arc length of a slot 30. To achieve higher tensioning force, the arc length of the slot 30 must be longer. As a result, the entire assembly will inevitably occupy a large space. Moreover, the longer the arc length of the slot 30 is, the longer the response time of the entire assembly will be, which implicates higher possibility of occupant injury at the moment of crash. In addition, since the pre-tensioning apparatus actuates the tensioning process by means of engagement between the actuating rod 16 and the mass block 17 and simultaneous disengagement of the actuating rod 16 from the seat belt supporting member 47, a serious consequence of malfunction of the pre-tensioning apparatus may occur if either of engagement/disengagement fails. Therefore, the service reliability of such a pre-tensioning apparatus is limited. To improve reliability, additional cost in design and manufacturing is required, causing degraded economic efficiency.
Another pre-tensioning apparatus is disclosed in Patent Document No. U.S. Pat. No. 4,768,809. In that pre-tensioning apparatus, a structure composed of two swing rods with adjacent ends hinged together are utilized to actuate the tensioning of the seat belt and restrain the seat belt at a restrained position. However, that structure has a common feature with the structure disclosed in GB2294866, i.e., it also utilizes an arc-shaped guide slot to guide the tensioning of the seat belt. Therefore, that structure also have the above-mentioned drawbacks, i.e., the tensioning force is limited by the guide slot structure and a large space is occupied.
Hence, it is desirable to provide a seat belt without the above-mentioned drawbacks. The seat belt should be able to exert appropriate and almost zero restraining force on the occupant so as to enable the occupant to act comfortably and move freely under essentially zero pressure of the seat belt in normally driving state, but can tension up the seat belt timely in case of any emergent or catastrophic event, and can release the seat belt automatically after the event. Moreover, the seat belt should have advantages such as simple structure, high reliability, easy replacement and adjustment, low cost, and wide applicability, etc.